ng linin connections.

64. Diamond-shaped tetrad with spindle-fibers attached; _a-a_, probably
halves of one univalent chromosome; _b-b_, halves of the other.

65. Dyad from anaphase of first maturation mitosis.

66-67. Metaphase of first maturation spindle, showing element _x_ in
different positions.

68. Late anaphase of same.

69-70. Equatorial plate of first maturation spindle, 23 chromosomes and
element _x_ below, in fig. 69.

71. Chromatin massed at poles of spindle; element _x_ isolated at one
pole.

72-73. Two resting spermatocytes of the second order, one containing
element _x_, the other not.

74-76. Successive stages of breaking down of element _x_.

77. Prophase of second division; dyads evident, but no sign of _x_ in
this or following stages.

78. Second spermatocyte division--metakinesis.

79. Same; late anaphase.

[Illustration: STEVENS. PLATE II.

N. M. S. del.

STENOPELMATUS.]

PLATE III.

_Stenopelmatus._

FIG. 80. Telophase of second maturation mitosis.

81. Young spermatid, showing spindle-remains at _s_.

82. Spermatid showing a conspicuous chromatin element in nucleus, and
spindle-remains (_s_) elongated.

83. Spermatid, showing centrosome (_c_) and divided spindle-remains (_s_
and _a_).

84. Older spermatid, showing centrosome (_c_), axial fiber of tail, and
spindle-remains (_s_).

85. Spermatid, showing acrosome material (_a_) migrating to side of
nucleus opposite centrosome.

86. Slightly older spermatid.

87. Later stage of spermatid, showing condensed chromatin, elongated
centrosome (_c_), acrosome material (_a_), and spindle-remains (_s_).

88-89. Older spermatids, showing formation of acrosome (_a_) and middle
piece (_m_).

90-92. More advanced stages.

93. Mature spermatozoon.

_Blattella germanica._

FIG. 94. Somatic cell from egg follicle, 23 chromosomes.

95. Spermatogonium, showing chromatin element (_x_) associated with a
nucleolus (_n_).

96. Same, prophase of mitosis.

97. Equatorial plate of spermatogonial mitosis, 23 chromatin elements.

98. Young spermatocyte, showing centrosome (_c_) and U-shaped element
(_x_).

99. Young spermatocyte, element _x_ attached to one end of a long, fine
spireme.

100. Coarser spireme stage.

101-103. Bouquet stage.

104-105. Later spireme stage.

106. Various forms assumed by the combined nucleolus and element _x_;
last figure from a giant cell.

107. Segmenting spireme.

108. Similar s